1. Field of the Invention
The present invention is in the field of electrical inductors, and more specifically relates to apparatus for assembling and for electrically calibrating laminated core inductors.
2. The Prior Art
In U.S. Pat. No. 2,055,175, issued Sept. 22, 1936 to Franz, there is shown a method and apparatus for making laminated cores and for adjusting them.
Two separated stacks of E-shaped laminations are built up, and the laminations of each stack are held together by a coating of adhesive applied to the exposed edges of the laminations. The adhesive is described as being a viscous and relatively quick-drying cement sufficiently thick and viscous not to be drawn in between the laminations by capillary attraction, but to remain on and adherent only to the edges of the laminations. The adhesive permits the stacks of laminations to be handled as self-coherent units. The lamination of the two stacks do no overlap. Franz does not disclose apparatus to facilitate stacking of the laminations. The two stacks of laminations are used as the two halves of the core of the inductor.
The inductor includes, in addition to the stacks of laminations, a coil which has been wound on a spool. As described in the Franz patent, a mass of still-viscous adhesive is placed inside the spool, and the central legs of the E-shaped stacks are then inserted into the spool from opposite ends. An air gap is left between the ends of the legs.
The assembly is then placed in an apparatus which includes a pair of wedges which are used in a controlled manner to force the stacks of laminations apart until the desired electrical characteristic is achieved. Franz does not describe the electrical calibration apparatus and method used, but merely states that a testing circuit is employed to determine when the mutual inductance of the windings takes on its desired value as the core halves are driven apart by the wedges. Thereafter, the assembled and calibrated inductor is left in the calibrating apparatus so that the wedges of that apparatus will resist the tendency of the adhesive to draw the core halves together as the adhesive dries. After the adhesive has dried, the finished coil is removed from the calibrating apparatus.
The method disclosed by Franz produces inductors at an unacceptably low rate because the inductors must remain within the apparatus until the adhesive has set, as taught by Franz. The present invention is based on a discovery which overcomes the limited production rate.
In U.S. Pat. No. 3,820,238, issued June 28, 1974 to Caputo et al. there is disclosed a method of constructing inductors using F-shaped laminations. The laminations are bolted together in spite of the admonition of Franz that mechanical compression of the laminations tends to adversely affect the permeability of the core.
In accordance with the method disclosed by Caputo et al., the laminations forming the opposite halves of the core are interleaved but with the portions of the laminations defining the air gap spaced apart sufficiently that a spool bearing the winding can be inserted between those portions. Next, the laminations forming each of the halves of the core are bolted together, so that the opposite halves of the core each can be moved as a unit. Thereafter, the coil-bearing spool is positioned in the air gap and the opposing halves of the core are pressed together, narrowing the air gap. Caputo et al. do not disclose an electrical means for determining when the proper air gap has been achieved. After the air gap has been adjusted, the laminations are clamped together by tightening the superposed laminations with nuts disposed on bolts.
The range of inductance values which can be obtained with the method of Caputo et al. is severely limited by the bolt holes in the laminations, which determine the width of the air gap. This, combined with the absence of any means for calibrating the inductance of the unit electrically, indicates that Caputo et al. are mainly concerned with assembling non-precision inductors having an inductance determined by the spacing of the holes in the laminations, rather than inductors having a precisely calibrated inductance determined by controlled adjustment of the air gap.
In U.S. Pat. No. 3,355,689, issued Nov. 28, 1967 to Paddison et al., there is shown a core formed of laminations having slots and holes in them to permit adjustment of the air gap.
The laminated core is stacked within the spool. Paddison et al. do not disclose apparatus to facilitate stacking of the laminations. The assembled coil is then adjusted by means of a screwdriver-like tool which alters its electrical properties as desired. Paddison et al. state that calibration of the electromagnet is effected by applying and measuring a voltage and a current to the coil while simultaneously adjusting the air gap with the special tool. After the coil has been calibrated, the laminations are bolted together. The method used by Paddison et al. requires that the laminations be provided with holes of the proper size, shape and location and does not lend itself to the production of precision inductors because the laminations are bolted together after the calibration is performed, and this tends to introduce inaccuracies.
Thus, it is seen that none of the methods known to the prior art is entirely satisfactory from the standpoint of ease of production or accuracy of calibration.
Machines for automatically stacking laminations are disclosed in U.S. Pat. No. 3,423,814 to Davis, U.S. Pat. No. 3,634,919 to Nieder, and U.S. Pat. No. 3,798,735 to Macchione. Machines of this type have a tendency to jam. With some of the machines it is not possible to stack more than, say, 90 percent of the laminations; the remaining laminations have to be inserted by hand.
As will become apparent, the present invention is not a machine for automatically stacking laminations. Instead, the present invention includes a fixture to facilitate manual stacking and calibration.